Yup. Happened to me with the stupid m6x1.00. Good for the rear mount, but I redrilled and rethreaded for 5/16 bolts for the bottom. Excellent fix to do, just gotta go slow and careful.
I have never milled one that I had the piston hit the head, although I've had to add a extra head gasket to keep the compression ratio down. We're not talking about but a few thousands if that much. ONLY take enough off so you can see shiny new surface. I guarantee that you will see it the first time you rub the head against the sandpaper. If you have stock studs/nuts you can wait till it blows a gasket, I suspect that it would do that sooner or later. Although some haven't. On my first build and thinking that there was some sort of QC, I blew a head gasket 5 miles from the house. Limped home...still have the gasket as a reminder. This all took place before joining the forums.
First, there is no "O" ring supplied with the kit. This is a mod as the union is prone to have a intake leak. Next, I don't remember the "O" size, if you have a NAPA store around they will have a assortment set (you can buy just 1). And, just take the carburetor with you, find a gasket will fit. OH and with a proper fit the "O" ring won't get sucked in, the "O" ring is the same size as the intake itself.
Flat against the bolt head, lock washers just before the nut. I use no other washers. The idea is to keep the nut from coming loose. If you have the plate, a washer, a lock washer, then the nut, the first flat washer has a possibility to spin...use of lock nuts are best.
